<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <!-- 选中的颜色       -->
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" ref="progressBtn"
           @touchstart.prevent="progressTouchStart"
           @touchmove.prevent="progressTouchMove"
           @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>

</template>
<script>

import {prefixStyle} from 'common/js/dom'
const progressBtnWidth = 16
const transform = prefixStyle('transform')
export default {
  props:{
    percent:{
      type: Number,
      default: 0
    }
  },
  name: "progress-vue",
  created() {
    this.touch = {}
  },
  methods:{
    progressClick(){

    },
    progressTouchStart(e){
      this.touch.initiated = true
      this.touch.startX = e.touches[0].pageX
      this.touch.left =this.$refs.progress.clientWidth

    },
    progressTouchMove(e){
      if (!this.touch.initiated){
        return
      }
      const deltaX =  e.touches[0].pageX -  this.touch.startX
      const offsetWidth = Math.min(this.$refs.progressBar.clientWidth - progressBtnWidth,
          Math.max(0, this.touch.left + deltaX))
      this._offset(offsetWidth)
      this.$emit('percentChanging',  this._getPercent())
    },
    progressTouchEnd(){
      this.touch.initiated = false;
      this._triggerPercent()
    },

    _triggerPercent () {
      this.$emit('percentChange', this._getPercent())
    },
    setProgressOffset(percent){
      if (percent >= 0 && !this.touch.initiated) {
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
        const offsetWidth = percent * barWidth
        this._offset(offsetWidth)
      }
    },
    _offset (offsetWidth) {
      this.$refs.progress.style.width = `${offsetWidth}px`
      this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`
    },
    _getPercent(){
      const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
      return this.$refs.progress.clientWidth / barWidth
    }
  },
  watch:{
    percent(newPercent){
      this.setProgressOffset(newPercent)
    }
  }
}
</script>

<style lang="stylus" scoped>
@import "~common/stylus/variable"
.progress-bar
  height 30xp
  .bar-inner
    position relative
    top 13px
    height 4px
    background: rgba(0, 0, 0, 0.3);
    .progress
      position absolute
      height: 100%;
      background: #ffcd32;
      width 40%
    .progress-btn-wrapper
      position: absolute
      left: -8px
      top: -13px
      width: 30px
      height: 30px
      .progress-btn
        position: relative;
        top: 7px;
        left: 7px;
        box-sizing: border-box;
        width: 16px;
        height: 16px;
        border: 3px solid #fff;
        border-radius: 50%;
        background: #ffcd32;

</style>
